Black-throated Blue Warbler

Distribution and Abundance

• BBS Map
• Breeding range northeastern United States and southeastern Canada; also in the southern Appalachian Mountains at higher altitudes. 
• Prior to European colonization, this species presumably had a wide distribution in the then extensive forests of northeast United States and southern Canada. As these forests were cleared in the 17th and 18th centuries (Irland 1982), suitable breeding habitat for this warbler shrank considerably. However, with the subsequent abandonment of farmland in New England and other parts of the Northeast from mid-19th century to present, forested habitat increased again (Litvitas 1993) and breeding habitat for this species is probably more extensive now than it was 100-150 years ago.
• BBS data from 1966-1991 indicate populations are stable. At present, generally no sign of major decline for this species in the main parts of its range, at least within suitable habitat. However, numbers declined significantly from 1982-1991 at range margins including Minnesota.
• Winters primarily in the Greater Antilles; also in the Bahamas. 

Habitat

• Breeds mainly in large, more or less continuous tracts of relatively undisturbed deciduous or mixed deciduous-coniferous forests. These forests are usually dominated by maples, birches, beech, and other northern hardwoods, with varying amounts of hemlock, spruce and fir.
• In Wisconsin, of 116 observations from 1995-2000 where habitat was reported, 84.5% were in upland hardwood forest, particularly maple, or upland mixed forest (WSO 2002). In Michigan, this species breeds most commonly in mesic deciduous forest dominated by sugar maple; also widespread, but much less numerous, in mesic mixed hardwood-conifer forest (Brewer et al. 1991).
• Often in hilly or mountainous terrain, perhaps because these are the only places where such large tracts of unbroken forest occur. In New York, occurs mainly above 300 m (Anderle and Carroll 1988); in New Hampshire, most abundant at elevations of 400-700 m; similarly in Vermont (Laughlin and Kibbe 1985).
• Forests most suitable for breeding contain a relatively thick undergrowth of dense, usually deciduous or broad-leaved evergreen shrubs; the plant species varies geographically. In the mountains of New Hampshire and Vermont, mostly hobblebush along with small saplings of sugar maple, beech, striped maple, red spruce and balsam fir (Laughlin and Kibbe 1985, Steele 1992). In other areas, mountain laurel, rhododendron, creeping yew, deciduous bushes, small saplings and tiny conifers (Bent 1953). 
• Selection of habitats with a dense shrub layer seems most closely related to nesting requirements and not to foraging needs or other factors (Holway 1991, Steele 1993). Nest site usually located in dense shrub layer of either deciduous or mixed coniferous-deciduous habitat. Frequently in broad-leaved evergreen shrubs, conifer saplings, deciduous shrubs, or deciduous saplings. Nest sometimes in a cluster of dead leaves, for instance among the dry foliage of a large branch or tree that has recently fallen (Nice 1930, Walkinshaw and Dyer 1953). 
• During migration, remains mostly in shrubby or forested habitats including forest edges, riparian woodlands, and other well-vegetated habitats, including parks and gardens (Bent 1953). Also, well-developed upland or riparian forests (Parnell 1969).
• Winter habitat generally dense tropical forests and woodlands, ranging from near sea level to high elevations (Holmes et al. 1989, Sliwa 1991, Wunderle 1992, Wunderle and Waide 1993). Occurs in second-growth habitats as long as they contain woody trees and dense understories (Lack and Lack 1972).

Behavior

• Diet insectivorous during breeding season. During winter, feed on insects and small berries and fruits.
• Most birds are solitary and generally intolerant of the approach of a conspecific of the same sex. Upon arrival on breeding grounds, males move around covering large areas (5-10 ha) before settling. Territorial disputes occur frequently. Females also chase one another.
• Territory sizes ranges from 1-4 ha, depending on habitat, being smallest where the shrub layer is dense and heterogeneous (Steele 1992).
• Most breeding males are monogamous; polygyny does occur, but at low and variable levels ranging from 0-15% (Petit et al. 1988, Holmes et al. 1992). Mate guarding appears to be frequent in this species, with the male remaining close to the female.
• When flushed from nest, female performs distraction display.
• Forage alone, although members of pair sometimes forage near one another.
• No evidence for interspecific territoriality, although some interspecific aggression occurs.
• In winter, this species is mostly solitary, occupying more or less exclusive home ranges or territories (Holmes et al. 1989, Wunderle 1992).

Parasitism and Predation

• Infrequently parasitized by Brown-headed Cowbird (Friedman et al. 1977, Friedman and Kiff 1985).
• This species may be less subject to cowbird parasitism because of its preference for nesting in large tracts of relatively undisturbed forest. In Wisconsin, of 477 confirmed Brown-headed Cowbird observations from 1995-2000, Black-throated Blue Warbler was not indicated as a host species (WSO 2002).
• Adults preyed upon by raptorial birds.
• Eggs and nestlings taken by Blue Jays and Sharp-shinned Hawks; also by red squirrels and eastern Chipmunks (Rodenhouse 1986, Reitsma et al. 1990).

Conservation and Management

• This species does not breed in young clear-cuts or second growth, but becomes common once canopy is well-developed and shrub layer is dense, usually greater than 50 yr following clear-cutting (Holmes 1990).
• Appears to be equally common in both managed and unmanaged northern hardwoods forests (Welsh and Healy 1993). Densities not significantly affected by selective logging activities (Webb et al. 1977) or by forest degradation (Darveau et al. 1992) as long as there is a dense shrub layer and relatively complete canopy cover.
• Area-sensitive, occurring mainly in tracts greater than 100 ha (Robbins et al. 1989).
• The two major factors affecting breeding success for this species are food and predation on eggs and nestlings (Rodenhouse 1986, Holmes et al. 1991, Rodenhouse and Holmes 1992).
• BBS trend results from 1966-2000 (Sauer et al. 2001) in the Northern Spruce-Hardwoods region indicate the Black-throated Blue Warbler may have increased in this region  (1.7, p=0.40 Trend Graph S28), as is the case in the Great Lakes Transition region (6.8, p=0.11 Trend Graph S20). Survey-wide (US and Canada), this species has remained stable (0.9, p=0.42 Trend Graph SUR).

References

• Anderle, R.F. and J.R. Carroll, eds. 1988. The atlas of breeding birds of New York state. Cornell University Press, Ithaca, N.Y.
• Bent, A.C. 1953. Life histories of North American wood warblers. U.S. Natl. Mus. Bull. 203.
• Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding birds of Michigan. Michigan State University Press, East Lansing.
• Friedman, H. and L.F. Kiff. 1985. The parasitic cowbirds and their hosts. Proc. West. Found. Vert. Zool. 2.
• Friedman, H., L.F. Kiff and S.J. Rothstein. 1977. A further contribution to knowledge of the host relations of parasitic cowbirds. Smithson. Contrib. Zool. No. 235.
• Holmes, R.T. 1990. The structure of a temperate deciduous forest bird community: variability in time and space. Pp. 121-140 in Biogeography and ecology of forest bird communities (A. Keast, ed.). SPB Academic Publ., Hague, Netherlands.
• Holmes, R.T., T.W. Sherry, P.P. Marra and K.E. Petit. 1992. Multiple-brooding, nesting success, and annual productivity of a neotropical migrant, the Black-throated Blue Warbler, in an unfragmented temperate forest. Auk  109:321-333.
• Holmes, R.T., T.W. Sherry and L.R. Reitsma. 1989. Population structure, territoriality and overwinter survival of two migrant warbler species in Jamaica. Condor 91:545-561.
• Holmes, R.T., T.W. Sherry and F.W. Sturges. 1991. Numerical and demographic responses of temperate forest birds to annual fluctuations in their food resources. Pp. 1559-1567 in Acta XX Cong. Internat. Ornithol.
• Holway, D.A. 1991. Nest site selection and the importance of nest concealment in the Black-throated Blue Warbler. Condor 93:575-581.
• Irland, L.C. 1982. Wildlands and woodlots - a story of New England's forests. Univ. Press New England, Hanover, NH.
• Lack, D. and P. Lack. 1972. Wintering warblers in Jamaica. Living Bird 11:129-153.
• Laughlin, S.B. and D.P. Kibbe. 1985. The atlas of breeding birds of Vermont. Univ. Press New England, Hanover, NH.
• Litvitas, J.A. 1993. Responses of early successional vertebrates to historic land use changes. Conserv. Biol. 7:866-873.
• Parnell, J.F. 1969. Habitat relations of the Parulidae during spring migration. Auk 86:505-521.
• Nice, M.M. 1930. A study of a nesting of Black-throated Blue Warblers. Auk 47:338-345.
• Petit, K.E., M.D. Dixon and R.T. Holmes. 1988. A case of polygyny in the Black-throated Blue Warbler. Wilson Bull. 100:132-134.
• Robbins, C.S., D.K. Dawson and B.A. Dowell. 1989. Habitat area requirements of breeding forest birds of the Middle Atlantic states. Wildl. Monogr. 103:1-34.
• Rodenhouse, N.L. 1986. Food limitation for forest passerines: effects of natural and experimental food reductions. Ph.D. diss., Dartmouth Coll., Hanover, NH.
• Rodenhouse, N.L. and R.T. Holmes. 1992. Food limitation for breeding Black-throated Blue Warblers: results of experimental and natural food reductions. Ecology 73:357-372.
• Sauer, J.R., J.E. Hines and J. Fallon. 2001. The North American Breeding Bird Survey, Results and Analysis 1966-2000. Version 2001.2, USGS Patuxent Wildlife Research Center, Laurel, MD.
• Sliwa, A. 1991. Winter geographic and habitat distributions of two migratory warblers (Parulinae) in Jamaica. W.I. M.Sc. thesis, Berlin Free Univ., Berlin, Germany.
• Steele, B.B. 1992. Habitat selection by breeding Black-throated Blue Warblers at two spatial scales. Ornis Scand. 23:33-42.
• Steele, B.B. 1993. Selection of foraging and nesting sites by Black-throated Blue Warblers: their relative influence on habitat choice. Condor 95:568-579.
• Walkinshaw, L.H. and W. Dyer. 1953. Nesting of the Black-throated Blue Warbler in Michigan. Jack-Pine Warbler 31:47-54.
• Webb, W.L., D.F. Behrend and B. Saisorn. 1977. Effects of logging on songbird populations in a northern hardwoods forest. Wildl. Monogr. 55:1-35.
• Welsh, C.J.E. and W.M. Healy. 1993. Effect of even-aged timber management on bird-species diversity and composition in northern hardwoods of New Hampshire. Wildl. Soc. Bull. 21:143-154.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.
• Wunderle, J.M., Jr. 1992. Sexual habitat segregation in wintering Black-throated Blue Warblers in Puerto Rico. Pp. 299-307 in Ecology and conservation of neotropical migrant landbirds (J.M. Hagan III and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Wunderle, J.M., Jr. and R.B. Waide. 1993. Distribution of overwintering nearctic migrants in the Bahamas and Greater Antilles. Condor 95:904-933.